Armored electric heating-unit.



C. P. MADSEN.

I ARMORED ELECTRIC HEATING UNIT.

APPLICATION FILED FEB. a, 1913.

1,093,792. Patented A r. 21, 1914 3 SHEETS-SHEET l.

0. P. MADSEN,

- ARMORED ELECTRIC HEATING UNL'I.

APPLICATION FILED FEB. 3, 1913. 1,093,792. Patented Apr. 21, 1914.

3 SHEETB-SHEET 2.

0. P. MADSEN.

ARMOBED ELECTRIC HEATING UNIT.

APPIEIGATION FILED FEBQ3, 1913. 1,093,792, Patented Apr. 21,191 L 3 SHEETSSHEET 3.

UNITED L STATES PATENT OFFICE.

CHARLES P. MADSEN, OF CHICAGO, ILLINOIS, ASSIGNCR TO THE MICHIGAN STOVE COMPANY,

A CORPORATION OF MICHIGAN.

ABMORED ELECTRIC HEATING-UNIT.

Specification of Letters Patent.

Application filed February 3, 1913. Serial No. 745,936.

To all whom it may concern:

- Be it known that I, CHARLES P. MADSEN, a citizen of the United States of America, and a resident of Chicago, county 0 Cook, and State of Illinois, have invented certain new and useful Improvements in Armored Electric Heating-Units, of which the following is a specification.

The main objects of provide an improved construction for electric heating units; to provide improved and more etlicient and durable means for protecting such units against electrical and mechanical injury; to provide an improved form of armor for the heating element; to provide improved terminal structures for connecting such units to the-source of current; to provide improved means for protecting the terminal connections from being short-circuited by liquid spilled thereon, or

from contact with other articles likely to cause either a short-circuit or mechanical injury thereto; to provide an armored electric heating unit which will operate at a higher emissivity rate, and to provide a composite flexible dielectric medium suitable for high temperature conditions.

\Vhat is herein meant by an armored unit is one in which the heat generating conductor is protected against mechanical injury from jolts, blows or contact with external objects, and also against any accidental electrical contacts or short-circuits, although permitting the ready transfer and radiation of heat energy. A suitable armor for this purpose is one which is externally of such character as to be able to resist dis tort-ion and injury through contact with external objects, and which is internally of such character as to have good insulating properties and at the same time be capable of keeping moisture and air away from the heat generating conductor.

As far as I am aware no single substance has yet been found which would not become a conductor of electricity when exposed to moisture or upon temperature rising, except-in those-substances which are brittle and t erefore unsuitable in themselves to fully comply with the before mentioned conditions. Therefore. armored units are, in

resent practice, of composite structure bemg made up of a layer of electrical insulation having high thermal conductivity and an outer metallic shell.

this invention are to The chief difiiculties in constructing such a unit have been .to make such composite structure which will remain mechanically solid and moisture proof through expansion and contraction due to temperature changes, and to provide a terminalstructure which will be practically'proof against short-circuiting by the spilling of liquids on the unit and which will withstand the same or a higher temperature than the unit itself.

A construction accomplishing the foregoing objects and ayoiding the difiiculties referred to may be made according to the present invention, a specific embodiment of which is illustrated in the accompanying drawings, in which:

Figure 1 is a perspective view of a heat ing element and means for protecting the same and its terminals, especially arranged for use in an oven or broiler. Fig. 2 is a plan View of one end of the broiler with the heating units in place and showing a part of the mounting broken away to show one o the unit terminals. Fig. 3 is a front elevation of the heating element shown in Fig. 1 and shows the terminal and housing structure usedin connection therewith. Fig. 4 is a detail of the core which so orts the winding of the heating element. ig. 5 is a detail showing the manner in which the winding is applied to the core. Fig. 6 illustrates the manner of applying the terminal sleeves by means of which connection is made to an external source of current. Fig. 7 illustrates the innermost layer of insulating material. Fig. 8 is a similar view showing the same coated with an application of powdered insulating material or paste which fills the spaces between the armor and the other insulation, as well as all interstices in the latter. Fig. 9 is a detail of one of the hard, thin, smooth strips which are used to protect the layer of powder and enable the assembled internal parts of the unit to be inserted easily into the armor. Fig. 10 is a without its terminal connections. ig. 14 is Patented Apr. 21, 1914.

an enlarged sectional view of the heating unlt as shown in Fig. 12. F1g. 15 1s a detail of a modified terminal arrangement adapted for use with long units.

In the construction shown, the high resistance' conductor 1, which makes up the heating element proper, is in the form of a flat wire or ribbon wound in some of the usual ways as, for example, on a core 2 of insulating material, as for instance mica, and the terminal end portions 3 of the conductors 1 are then bent outwardly so as to extend lengthwise beyond the ends of the! winding. Notches 4 may be formed in the core" at the ends of the winding to facilitate turning the terminals outward toward the ends of the core.

Practically all of the difliculties usually encountered in making durable terminal connections with windings of high temperature alloys, such as are usually used in heating elements are overcome by providing thin metallic shields 5 in the form of wrappings or flattened tubes applied to the ends of the core and engaging the ends of the wire and forming enlarged extensionsthereof. These sleeves, great pressure, contact with the wire, the tubes to make large contact therewith. The portions of the conductor'within the terminal tubes, therefore, divide the current with the terminal tubes, and since the re when in place, are flattened under so as to make good electrical which extends into sistance of the conductor ribbon is relatively compared with that of the tubes, the

high

with the shields,

former, where in contact would carry practically no current if the contact .were perfect. On account of the relatively greater conductivity of the combined tn and conductor at this point, the terminal portions of the conductor will be kept at comparatively low temperature. Should, however, the electrical contact betweenthe conductor andthe tube become imperfect for any reason, the increased local resistance at this point might tend to cause the connection to become highly heated, but nevertheless it is practically impossible for it to burn out since it is protected from air by the sleeve, and the temperature would be kept relatively low on account" of the heat which would be carried away from it by the tube 5 ing the paper with a hard comparatively infusible finely pulverized substance 8 p'referably silica, which increases both the electric insulating strength and the heat conductivity of the asbestos wrapping.

In order to prevent displacement of the powder, and to otherwise facilitate the insertion of the heating element into the armor tube, two strips 9 of continuous hard, thin, smooth, non conducting material such as mica are fastened to opposite sides of the element, as illustrated in Fig. 11, these being cut to the form shown in Fig. 9 so as to completely cover both'faces of the portion of the element which is inclosed in the armor. The extremities of the strips 9 are secured by metal armor. segments or shields 10, which may be made 0 strips wrapped around the parts or may be made of flattened tubes. It will be noted from Figs. 11 and 12 that the. sleeves 10 and the mica strips 9 terminate a considerable distance inward of the perforated ends of the sleeves 5. The middle segment of the armor is a flattened tube 11 which snugly fits the heater unit parts when assembled, as in Fig. l2, and is slipped over these parts to a middle position, as illustrated in Figs. 12 and 13. The lower portion of the tube 11-,-which is shown inverted in Fig. 10, is somewhat shorter in length than the upper portion so that the top portion slightly overhangs the ends of the sleeves 10. The inner parts of the assembled element are ends of the tube 11. The extremities of the sleeves 5 preferably, but not necessarily, are then bent to a horizontal position in the same plane with each other, as illustrated in Figs. 12 and 13. This offsetting of the ends of the heating element and the corresponding joints in the armor, allow for longitudinal expansion and contraction of the various parts without causing rupture or distortion of the unit or its armor. The terminal end portions of the sleeves 5 are preferably perforated for receiving a screw or the like, and may be secured to rigid binding posts. On account'of the peculiar longitudinal form of the element the joint with the binding posts will be unaffected by expansion and contraction of the element.

fter the parts are assembled, as shown, the tube 11 is subjected to great pressure tending to further flatten it, and thereby causing it to exert a permanent pressure on the heating element and its insulation, thus increasing the thermal conductivity of the latter. By reason of the fact that the tube 11 is seamless or substantially integral on all sides, no amount of contraction and expansion under temperature changes can cause it to become distorted or to open up so as to admit moisture through its walls. Even though there be differences in the expansibitia; of the various parts under temstruction as illustrated in is given to the tube =p'er end of the member case the ends of the armor 11 are not undercut and the flexible armor 10 is omitted since the armor 11 extends into the side of the terminal housing 15. In order to allow for the greater degree of expansion and contraction which would arise in a long unit, the terminals 5 of the heating element'are offset by abrupt 90 bends. This gives great flexibility and allows for all of the required expansion and contraction without exerting strains which would tend to loosen up the connection of the element to the binding post 17.

Although but one specific embodiment of my invention is herein shown and described, it is to be understood that various details of construction may be changed somewhat or omitted without departing from the spirit of my invention as defined in the following claims.

I claim:

1. An electric heating unit comprising a heating element, a covering of porous insulating fabric therefor, a thin filling of powdered insulating material applied to the latter, and aclose fitting metallic armor tightly inclosing and compressing the same, said powdered material filling all' the minute spaces between said heating element, insulation and armor, and filling the pores or interstices of said insulation.

2. An electric heating unit, comprising a fiat core of insulating material, a winding of high resistance conducting material mounted on said core, a wrapping of insulating material inclosing said winding, a pair of strips of comparatively stitt matc rial longitudinally disposed and secured to opposite fiat sides of said wrapping of insulating material, and a flat tubular shell tightly holding and compressing said parts and serving as an armor therefor.

the permanent set which 11 in the final flattening will ofiset such difference in expansion to a sufiicient extent to prevent the tube from becoming loosened and thus providing space for the entrance of moisture.

The downwardly inclined terminal armor sections 10 are made of relatively thin material and are preferably telescoped slightly within the ends perature changes,

of the heavier middle armor section 11 in assembling. Then when the ends of the element projecting from the section 11 are bent down the inner ends of section 10 are also bent correspondingly thus providing a most secure and efficient o1nt.

In the form shown the terminal connections on opposite sides of the heater respectively are inclosed, each set within a metallic casing which forms an extension of the armor tubes 11,"as illustrated in Figs. 1 and 2. In these views numeral 15 designates a trough-shaped casing shell or housing member which is formed'of such length as to inclose either one or a series of terminals, depending on the size of heater desired. covering 16 of suitable shape closes the up- 15 and completes the be noted that the covering 16 overhangs the sides of the trough 15 and slopes downward at all sides, so as to shed any liquid which might be spilled on it, and that the armor tube 11 extends into a suitable opening in the side of the cover fitting snugly in said opening so as to avoid as much as possible the leakage of liquid into the housing. Any liquid which might leak in'would run down along the inclined sleeve 10 and would not tend to enter the interior of the armor 11. The binding post 17 is thoroughly insulated from the walls of the. housing,-as shown, and the bottom of the housing is pressed up in the vicinity ofthe binding post, so that any liquid leaking into the housing would be deflected from the binding post and thereby the likelihood of such liquid short-circuiting the ser1es of binding posts would be avoided. Fitting into such upward pressed portion is a correspending upward pressed portion in the oven floor 18 upon which the housings 15 are mounted. The bindin posts 17 with their nuts and washers ho d the floor and housings closely together so that liquids spilled upon the floor 18 cannot leak through into the housing or through the floor into the connections beneath, as for instance to the connection of the electric supply wire 19 to the lower end of the binding post 17 The hereinbefore described construction is well adapted to heating units of short length, say up to six or eight inches in length, but in places where it is desired to housing. It is to element having a thin fibrous fireproof insulating covering permeated with a powdered refractory insulating material.

4. A heating unit, comprising a coil of resistance material covered with a wrapping of fibrous fireproof insulating material, said wrapping being permeated and covered by a continuous layer of powdered refractory insulating material.

5. A heating unit, comprising a coil of resistance material covered with a wrapping of fibrous fireproof insulating material, said wrapping being covered by a continuous layer of powdered silica.

6. A heating unit, comprising a 'coil ofresistance material covered with a wrap ping of fibrous fireproof insulatingmaterial, said wrapping being covered by a continuous layer of powdered insulating material have units of considerably greater length adapted on being heated to form an air tight it is preferred to modify the terminal conseal for the heating element.

Fig. 15. In this 7. A heating unit, comprising a coil of 3. A heating unit, comprising a heating resistance matbrial covered with a wrapping of fibrous insulating material, said wrapping being covered by a continuous layer of powdered refractory insulating material and an ope -ended armor of comparatively rigid material adapted to be slipped endwise over and inclose the whole, there being also a layer of comparatively hard and smooth insulating material extending along the exposed surfaces of said layer of powdered material and" adapted to protect the powder when the coil is being inserted into said armor.

8. A heating unit, comprising a core of insulating material, a winding of resistance material thereon, a wrapping of flexible insulating material inclosing said winding, a layer of powdered insulating material surrounding said wrapping, sheets of mica secured against the outside of said layer of powdered material, metal sleeves confining the ends of said mica strips, and a tubular armor inclosing the parts between said sleeves.

9. A heating unit, comprising a core of insulating material, a winding of resistance material thereon, a wrapping of flexible insulating material inclosing said winding, a layer of powdered insulating material surrounding said wrapping, strips'of mica secured against the outside of said layer of powdered material, metal sleeves confining the ends of said strips, and a .substantially seamless tubular armor inclosing the parts between said sleeves and overlapping the latter.

10. In an electric heating apparatus, the combination of a flat tubular armor, an insulated heating element extending through the same and having electric terminal end portions projecting beyond the ends thereof, said terminal end portions being downwardly ofl'set out of the plane of said tubular armor, binding posts securing said terminal end portions, and a housing at each end inclosing said binding posts and forming substantially a continuation of said armor at each end thereof, said housings having their-bottom walls perforated to receive said binding posts, and the perforated portions thereof belng formed upwardly out of the plane of the bottom of said housings and the top of said housings overlapping said armor, all being arranged to prevent short-circuiting of said terminals by. liquid spilled on said armor.

11. An electric heating unit, comprising a core of insulating material, a winding of resistance wire thereon, flattened sleeves fitting over the ends of said core in intimate contact with the ends and 0f the winding adapted to serve as enlarged terminals therefor, insulation covering said winding and the adjacent ends of said sleeves, and an armor surrounding said insulated parts and an armor surrounding being made up of overlapping tubular segments disposed at an angle to each other.

12. An electric heating unit comprising a core of insulating material, a winding of resistance wire thereon, flattened sleeves fit- 7 ting over the ends of said core in intimate contact with the ends of the winding and adapted to serve as enlarged terminals therefor, insulation covering said windin and the adjacent ends of said sleeves, said s eeves being bent to offset the outer extremities thereof from the plane of the winding, and said insulated arts overlapping tu ular at the bends in said 13. In a device of the class described, a horizontally disposed floor plate, in combination with an armored heating element having supporting end terminals bent downwardly and secured by insulating means to said floor plate to uphold and support the heating element suitably spaced apart from said plate, substantially as and for the purpose set forth.

14. An armored heating element havin a rigid central body armor, and a flexible and being made up of segments and meetin sleeves.

- armor extending beyond the rigid armor to allow for bending the ends of the said element into another plane and still be protected at the bent portion.

15. An armored heating element having a resistance element, insulation therefor, a rigid central armor, and a flexible armor projecting beyond the rigid armor, the reo sistance element and insulating material extending beyond the flexible armor.

16'. An armored heating element arranged to mount on terminalposts and having a rigid body armor, and a flexible projecting 1 5 armor portion bent so that the expanding of the element by heat may be compensated for' without'moving the ends in contact with the terminal posts.

.17. In a device of the class described, an

electric heating element in combination with a. protective housing-arranged to receive a terminal of said heating element, a floor element upon which said housing is mounted, and a binding ost for supporting said terminal within t e housing and arranged to securely hold said housing in place upon said floor, element. h

18. In a device of the class described, a heating element in combination with a ter- 12o minal housing formed to receive a terminal of said heating element, and a binding post arranged to project upward into said housing through its bottom and insulated therefrom to support said terminal, said bottom 126 being somewhat elevated around the said binding post to deflect moisture therefrom and the roof of said housing being arranged to deflect moisture.

19. In a device of the class described, a 130 floor element and a terminal housing'mountof moisture spilled upon the said floor ele- 10 ed thereon in combination with an insulated ment. binding post projecting upward through Signed at Chicago this 11th da; of J angegistering peirforations in the floor and the uary 1913.

ase of said ousing to support a termina I therein, said floor and Lbase'being raised at CHARLES MADSEN' andadjacent to the point of entry of the Witnesses: said binding post to deflect moisture from EUGENE A. RUMMLER,

the insulated post and to prevent entrance M. IRENE HUTCHINGS. 

